Big job, no problem. Over four acres of sand cement screed

Commissioned by Heijmans, all concrete floors in the new courthouse were provided with sand-cement screeds. "At over 42,000 square meters, this was indeed one of the largest jobs in our history," says Heijmans. 

A sand-cement screed is also the solution for NACH that makes any floor finish possible for a concrete shell. In this case, those finishes ranged from large natural stone floor tiles (1.2 m x 1.2 m) in the public areas to carpeting in the offices. Those large tiles in particular required extra-flat screeds. "Flatness class 2, according to NEN 2747," Van den Heuvel specifies. "But the office floors are also finished nicely flat. In them are wide cable ducts that were tightly smoothed so that the floor covering could be laid over them in one go."

Multiple shifts

For floor construction on such projects, Van den Heuvel uses work crews with trucks that function as small concrete plants on site. "Such a truck contains sand, cement and a mixing plant and pumps the mix through a spray hose to the desired location," Van den Heuvel explains. "Depending on the floor thickness, which here is between seven and eight centimeters, this allows us to lay 250 to 300 square meters of screed per crew in one day. Because several of NACH's floors are much larger, they were laid in sections. To deal with time constraints in the schedule, we were on site with sometimes two or three shifts and trucks." 

Shrinkage reinforcement

The screeds were largely laid adherent to the concrete subfloors. Only in the basements was an intermediate layer of insulation applied to eliminate cold bridges. Shrinkage reinforcement was applied everywhere to prevent cracking. Underfloor heating was installed locally, already prepared by the contractor. Two strengths were applied. Van den Heuvel: "In the basements, a number of floors on which installations will be placed are of strength class C30 and the same applies to some floors in public areas. Otherwise, C20 was applied everywhere. To gain some extra time, the last floors we laid incorporated drying accelerator."

All in all, an impressive project for Van den Heuvel's flooring contractors. "You're talking about acres of cement screeds seven, eight centimeters thick. That's a lot of cubic meters and man hours of preparation, pouring, floating and finishing. In any case, the result is something to be proud of. And the cooperation with the people from Heijmans went super again."